Electric Field Region Research Articles

Experimental study on the movement of non-spherical particles in nonuniform electric field

The deactivation of free particles is an important issue for improving the insulating capability and reliability of high-voltage systems. In this work, we carry out experiments to investigate the electromechanical behavior of the non-spherical conducting particles for different particle orientations on either bare or coated electrode. Spheroidal and wire-shaped particles are used for the experiments. The particle motion is observed for two principal orientations with respect to the applied electric field in air. The results show that on a bare electrode, both kinds of particles exhibit the liftoff motion when the particle axis is aligned with electric field gradient. The field nonuniformity enhances the upward rotation of the particle tip subjected to the higher electric field. When the particle axis is parallel with a constant field line, the wire-shaped particle is more readily to make a rolling motion to the region of stronger electric field in comparison with the spheroidal particle, which shows higher occurrence rate of liftoff. The motion onset electric field decreases with increasing field nonuniformity. On the insulated electrode, the wire-shaped particle shows exclusively the rolling motion, whereas the spheroidal particle may make a rolling motion or rotate horizontally so as to align its axis with electric field gradient.

Impact of permittivity and concentration of filler nanoparticles on dielectricpropertiesof polymer nanocomposites

Electrical properties of polymeric insulators can be improved by adding high-permittivity nanofillers. In this work, the aim is to analyse the effect of filler permittivity, its size, shape, concentration and the interparticle distance on the electrical properties of the nanocomposites. Nanocomposites are fabricated with four types of fillers and with various concentrations and the effect of various filler parameters on permittivity, breakdown strength and loss tangent of the nanocomposites are analysed. Simulation of electric field is used to demonstrate the increase in the volume of enhanced electric field region which affects the short-time breakdown strength. The effect of filler parameters on the electrical properties of the composite is demonstrated through experimental and theoretical analysis.

Electrical and nonlinear current-voltage characteristics of La-doped BiFeO3 ceramics

Multiferroic Bi1-xLaxFeO3(x=0, 0.05, 0.1, 0.2, and 0.3) ceramics with particle sizes of ~67–19nm were prepared by a simple co-precipitation method. The effects of La dopant on the microstructure, giant dielectric response, and electrical properties were investigated. The grain size of Bi1-xLaxFeO3 ceramics significantly decreased with increasing La doping ions. The Bi0.95La0.05FeO3 ceramic exhibited the highest leakage current density value. Interestingly, it strongly decreased as the concentration of La increased. The nonlinear coefficient of La doped BFO slightly decreased with increasing La. This shows a space-charge-limited conduction mechanism, which is involved in low electric field regions for all samples investigated. La substitution significantly enhanced the breakdown field. It was found that the potential barrier height at the grain boundary was slightly reduced from 0.3 to 0.16eV by substitution of La ions. Using impedance spectroscopy analysis, except for the Bi0.7La0.3FeO3 ceramic, the grain boundary resistance at room temperature was affected by dc bias, whereas the grain resistance of all samples was independent of dc bias. This result was well consistent with the variation in low-frequency dielectric constant and loss tangent value due to the effect of dc bias. These results were closely related to the existence of the interfacial polarization at the grain boundary.

Study on dielectric, optic and magnetic properties of manganese and nickel co-doped bismuth ferrite thin film

BiFeO3 (BFO), Mn (7.5%)-doped BFO (BFMO), Ni (7.5%)-doped BFO (BFNO), as well as Mn (3.75%) and Ni (3.75%) co-doped BFO (BFMNO) films were deposited on indium tin oxide (ITO)/glass substrates by sol–gel process. X-ray diffraction (XRD) analysis indicated that the BFO and BFNO presented single rhombohedral structure, while BFMO and BFMNO thin films presented tetragonal structure. The current density versus electric field (J–E) characteristics indicated that leakage conduction can be decreased with Mn and/or Ni doped. The films conduction mechanism of BFO and BFNO are space-charge-limited current in the high electric field region, while for BFMO and BFMNO is Ohmic’s conduction in all electric field region. The optical band gap of the BFO, BFMO, BFNO and BFMNO thin films are 2.18, 2.22, 2.3 and 2.32 eV, respectively. The inhomogeneous spin-modulated magnetic structure of BiFeO3 was modified by Mn and/or Ni substitution.

Sequential modelling of ICRF wave near RF fields and asymptotic RF sheaths description for AUG ICRF antennas

A sequence of simulations is performed with RAPLICASOL and SSWICH to compare two AUG ICRF antennas. RAPLICASOL outputs have been used as input to SSWICH-SW for the AUG ICRF antennas. Using parallel electric field maps and the scattering matrix produced by RAPLICASOL, SSWICH-SW, reduced to its asymptotic part, is able to produce a 2D radial/poloidal map of the DC plasma potential accounting for the antenna input settings (total power, power balance, phasing). Two models of antennas are compared: 2-strap antenna vs 3-strap antenna. The 2D DC potential structures are correlated to structures of the parallel electric field map for different phasing and power balance. The overall DC plasma potential on the 3-strap antenna is lower due to better global RF currents compensation. Spatial proximity between regions of high RF electric field and regions where high DC plasma potentials are observed is an important factor for sheath rectification.

Sustainable Electrospinning of Nanoscale Fibres

Electrospinning is an effective technology for the preparation of nano and micro scale fibres for diverse application in oil recovery, medical devices, and filters. It is achieved by injecting a charged solution of polymeric material through a needle into a region of high electric field. Under these conditions, the expelled jet follows a chaotic, whip-like trajectory towards a grounded collection plate. At low polymer concentrations, the high forces experienced by the jet prior to becoming grounded on the collection plate, result in the formation of undesirable discrete droplets of material, rather than fibres. At higher concentrations, above the critical entanglement limit for the polymer, the polymer chains are stretched and orientated whilst the solvent rapidly evaporates, delivering high aspect ratio fibres. The resulting mesh of overlapping fibres frequently has useful properties such as high surface area and porosity, which has led to their investigation for a range of applications including filtration membranes and tissue scaffolds. One of the major challenges in the development of electrospinning as a manufacturing technology is the use of organic solvents. Typically, fibres are spun from relatively dilute solutions containing 95% solvent. It is clear that systems which use water as a solvent offer many advantages in terms of safety, cost and sustainability. In this work we optimise the conditions for effectively preparing nano/micro fibres of polyethylene oxide from aqueous solutions. We contrast the fibres produced with those prepared using volatile organic solvents.

3D Simulation and Modeling of Ultra-fast 3D Silicon Detectors

3D detectors with very small electrode spacing can provide ultra-fast detection due to their extremely small charge collection time. Since the detector full depletion voltage and charge collection time are independent to the detector thickness, ultra-fast 3D detectors can be made relatively thick (or not too thin, ~200 μm) to ensure a large signal. The results of the 3D simulations and modeling of 3D silicon detectors with very small electrode spacing and relatively large thickness will be shown in this paper. The column spacing LP is in the range of 5 μm to 10 μm. At a bias voltage of only a few volts, the electric field in the detector can be large enough to ensure the carrier saturation drift velocity in most volume of the detector, and the detector charge collection time there can be as short as 10’s of ps. In this paper, we will analysis the simulated electrical characteristics of this detector structure through systematic 3D simulations using the Silvaco’s TCAD tool. Profiles of detector electric potential and electric field will be presented. We will investigate the region of low electric field (the “slow region”) in the detector. We will also exam whether the detector reach the breakdown condition at operation voltages suggested in this work.

平等電界領域における大気中球ギャップのULD現象低電位依存性

To the present, the ultraviolet radiation linear discharge (ULD) phenomenon was found in the sphere gap of the uniform electric field region. This phenomenon is the phenomenon which generates the linear discharge of the ultraviolet radiation region with the spark discharge. It became clear that ULD had the close relation for the phenomenon known until now as spark delay and irregular discharge phenomenon only.

平等電界領域における大気中球ギャップの不整放電現象の要因

By the present, uniform electric field region of the sphere gap is utilized for the high tension proofreading. Generally, the discharge voltage is difficult to get stabilized discharge voltage, when spherical electrode is used. Especially, beginning of use is discharged low-voltage, when there was long-time unused hour of spherical electrode, since there is a position which is easy to discharge the electron. Such discharge is known as an irregular discharge phenomenon. Therefore, pre-discharge, etc. is done near in the use.

Influence of initial velocity on trajectories of a charged particle in uniform crossed electric and magnetic fields

Magnetic and electric fields can cause a charged particle to form interesting trajectories. In general, each trajectory is discussed separately in university physics textbooks for undergraduate students. In this work, a solution of a charged particle moving in a uniform electric field at right angles to a uniform magnetic field (uniform crossed electric and magnetic fields) is reported; it is limited to particle motion in a plane. Specific solutions and their trajectories are obtained only by varying the initial particle velocity. The result shows five basic trajectory patterns, i.e., straight line, sinusoid-like, cycloid, cycloid-like with oscillation, and circle-like. The region of each trajectory is also mapped in the initial velocity space of the particle. This paper is intended for undergraduate students and describes further the trajectories of a charged particle through the regions of electric and magnetic fields influenced by initial condition of the particle, where electromagnetic radiation of an accelerated particle is not considered.

Fractal Model of a Compact Intracloud Discharge. II. Specific Features of Electromagnetic Emission

We examine the features of the electromagnetic emission of a compact intracloud discharge (CID) within the framework of the fractal approach [1] described in the first part of the article. Compact intracloud discharge is considered as the result of electric interaction of two bipolar streamer-type structures previously developed in the regions of a strong electric field inside the thundercloud. To estimate the electromagnetic emission of the discharge, the complex tree-like structure of the electric currents at the preliminary and main stages of CID was represented as the sum of a relatively slowly varying large-scale linear mean component and fast small-scale constituents corresponding to the initial formation of elementary conductive channels of the discharge tree. Mean linear current of the discharge is considered as an effective source of the VLF/LF emission at both the preliminary and main stages of a CID. Electrostatic, induction, and radiation components of the electric field at different distances from the mean current are calculated taking into account specific features of both stages of the discharge within the framework of the transmission-line model. It is shown that at the preliminary stage only the electrostatic component can mainly be detected, whereas at the main stage all the above components of the electric field can be reliably measured. Dependence of the radiation electric field at the main stage on the length of the discharge channel and propagation velocity of the current front is analyzed. It is found that due to the bi-directional expansion of the current at the main stage of a CID the radiation field pulse remains narrow in a wide range of discharge parameters. The small-scale currents corresponding to the initial breakdown between the neighboring cells of the discharge domain are considered as the sources of HF/VHF radiation. It is shown that HF/VHF emission at the preliminary stage is negligible as compared to emission at the main stage. It is also established that at the main stage, first, the HF/VHF emission burst correlates well with the initial peak of the VLF/LF electric field pulse and, second, its spectrum corresponds to the power law with an exponent between −2 and −1.

Bipolar resistive switching and conduction mechanism of an Al/ZnO/Al-based memristor

In this study, a direct-current reactive sputtered Al/ZnO/Al-based memristor device was fabricated and its resistive switching (RS) characteristics investigated. The optical and structural properties were confirmed by using UV–vis spectrophotometry and x-ray diffraction, respectively. The memristive and resistive switching characteristics were determined using time dependent current–voltage (I-V-t) measurements. The typical pinched hysteresis I-V loops of a memristor were observed. In addition, the device showed forming-free, uniform and bipolar RS behavior. The low electric field region exhibited ohmic conduction, while the Schottky emission (SE) was found to be the dominant conduction mechanism in the high electric field region. A weak Poole-Frenkel (PF) emission also appeared. In conclusion, it was suggested that the SE and PF mechanisms were related to the oxygen vacancies in the ZnO.

Electrical characteristics and conduction mechanisms of amorphous subnanometric Al2O3–TiO2 laminate dielectrics deposited by atomic layer deposition

Electric conduction mechanisms of amorphous Al2O3/TiO2 (ATO)-laminates deposited by atomic layer deposition with sub-nanometer individual layer thicknesses were studied in a large temperature range. Two characteristic field regions are identified. In the low field region (E ≤ 0.31 MV/cm), the leakage current is dominated by the trap-assisted tunneling through oxygen vacancies occurring in the TiO2, while in the high electric field region (E > 0.31 MV/cm) the Poole Frenkel (PF) hopping is the appropriate conduction process with energy levels depending on the temperature and the electric field. It is shown that the PF potential levels decrease with the applied ATO field due to the overlapping of the Coulomb potential. Amorphous ATO-laminates show the presence of two intrinsic potential energy levels ϕi, which are 0.18 eV for low temperature region and 0.4 eV at high temperature region. Oxygen vacancies are the main origin of traps, which is consistent with the principal mechanisms for leakage in ATO-laminates.

Measurement of the orientation of buffer-gas-cooled, electrostatically-guided ammonia molecules

The extent to which the spatial orientation of internally and translationally cold ammonia molecules can be controlled as molecules pass out of a quadrupole guide and through different electric field regions is examined. Ammonia molecules are collisionally cooled in a buffer gas cell, and are subsequently guided by a three-bend electrostatic quadrupole into a detection chamber. The orientation of ammonia molecules is probed using (2+1) resonance-enhanced multiphoton ionisation (REMPI), with the laser polarisation axis aligned both parallel and perpendicular to the time-of-flight axis. Even with the presence of a near-zero field region, the ammonia REMPI spectra indicate some retention of orientation. Monte Carlo simulations propagating the time-dependent Schrödinger equation in a full basis set including the hyperfine interaction enable the orientation of ammonia molecules to be calculated – with respect to both the local field direction and a space-fixed axis – as the molecules pass through different electric field regions. The simulations indicate that the orientation of ∼95% of ammonia molecules in JK=11 could be achieved with the application of a small bias voltage (17V) to the mesh separating the quadrupole and detection regions. Following the recent combination of the buffer gas cell and quadrupole guide apparatus with a linear Paul ion trap, this result could enable one to examine the influence of molecular orientation on ion-molecule reaction dynamics and kinetics.

Shunting effect in explosive electron emission

An explanation is given to the results of an experiment on studying the explosive electron emission in a wire-cathode diode where a strongly nonuniform energy deposition into the wire material was observed using an X pinch as a radiation source for projection x-ray imaging. The specific input energy, contrary to the well-known observations, was not a maximum at the wire end, i.e., in the region of the strongest electric field, and the wire explosion occurred in the bulk, distant from the end. This is accounted for by the contribution of the wire side surface to explosive electron emission and by the gas desorption from the wire intensely heated by a current of density 108 A/cm2. Thus, the space between anode and cathode (wire end) is bridged by two plasmas: one generated due to the explosive electron emission from the wire side surface and the other produced from the desorbed gas.

Verification of the plasma diffusion-wave propagation in an atmospheric-pressure plasma jet with the solution of a diffusion equation

The time-dependent solution of diffusion equation by the Fourier integration provides the axial diffusion velocity of a plasma packet, which is a key element of the plasma propagation in a plasma jet operated by the several tens of kHz. The plasma diffusion velocity is higher than the order of un ∼ 10 m/s at a high electric-field region of plasma generation and it is about the order of un ∼ 10 m/s at the plasma column of a low field region in a jet-nozzle inside. Meanwhile, the diffusion velocity is slower than the order of un ∼ 10 m/s in the open-air space where the plasma density flattens due to its radial expansion. Using these diffusion velocity data, the group-velocity of plasma diffusion wave-packet is given by ug ∼ cs2/un, a combination of the diffusion velocity un and the acoustic velocity cs. The experimental results of the plasma propagation can be verified with the plasma propagation in a form of the wave-packet whose propagation velocity is 104 m/s in a tube inside and is as fast as 105 m/s in the open-air space, thereby reconfirming that the theory of a plasma diffusion-wave is the origin of the plasma propagation in a plasma jet.

A compact model of the reverse gate-leakage current in GaN-based HEMTs

The gate-leakage behavior in GaN-based high electron mobility transistors (HEMTs) is studied as a function of applied bias and temperature. A model to calculate this current is given, which shows that trap-assisted tunneling, trap-assisted Frenkel-Poole (FP) emission, and direct Fowler-Nordheim (FN) tunneling have their main contributions at different electric field regions. In addition, the proposed model clearly illustrates the effect of traps and their assistance to the gate leakage. We have demonstrated the validity of the model by comparisons between model simulation results and measured experimental data of HEMTs, and a good agreement is obtained.

Dielectrophoretic Manipulation for Picking up and Relocating Single Cells By a Microdisk Electrode with Microcavity

The handing of single cells is important for investigating characteristics of individual cells. Dielectrophoresis (DEP) has been widely used as a manipulation tool for patterning and positioning of cells. The direction of the force depends on the relative polarizabilities of cells and suspending mediums, which induces cells to move towards or against the strong electric field region. Positive-DEP (p-DEP) is a force directed cells towards the region of electric field maxima, while negative-DEP (n-DEP) is a force to repel cells from the strong electric field. Thus, the target cells can be captured and released by DEP force. In this presentation, we demonstrate dielectrophoretic manipulation using a microdisk electrode with microcavity for picking up, positioning and relocating single target cells and also applied the present technique to the patterning with living cells by manipulating the individual cells. The needle type of Pt microelectrode tip (20 μm diameter) with the microcavity (10 μm depth) was mounted on a xyz micromanipulater. The tip was contacted to an ITO (Indium-Tin-Oxide) substrate. The tip was placed close to the target cell on the ITO substrate. The AC voltage with frequency for p-DEP (10 MHz) was then applied to the tip to capture the cell in the microcavity with a function generator, while the ITO was connected to the ground. The voltage was immediately turned off after trapping the cell. The captured cell was transferred to the desired position by moving the tip with the xyz micromanipulater and was released from the cavity by the repulsive force of n-DEP (1.0 kHz). The arrangements of the cells were obtained by repeating a series of procedures for each cell. The capture of the cells by p-DEP was investigated. The surface of the electrode was positioned at 50 μm right from the center of the target cell. When AC voltage (10 Vpp, 10 MHz) was applied, the cell began to direct toward the tip and moved to capture in the macrocavity at 16 s. The attractive force of p-DEP by the tip with microcavity can be applicable for trapping a single cell, since relatively high electric field was formed in the microcavity. The esterase activity in the trapped cells were investigated by staining the cells. The clear fluorescence signal observed from the trapped cell in the microcavity indicates that the cell is alive. The cell trapped in the microcavity was released by n-DEP. Again, the target cell directed toward the microcavity by attractive p-DEP force. After the voltage was turned off, the trapped cell remained in the microcavity. The trapped cell released gradually and positioned at the point of the tip after the voltage and frequency were switched to 2.0 Vpp and 1.0 kHz, respectively. The repulsive force caused by n-DEP directed the cell in microcavity toward the outside of the microcavity. The n-DEP force is useful to arrange the cells at the desired position precisely. The patterning with cells can be performed by the capture and release of individual cells with p- and n-DEP. We picked the target cell up in the microcavity by p-DEP. The trapped cell has been remained in the microcavity during the transfer to the desired position. After manipulation to the desired position, the trapped cell was then released from the microcavity by n-DEP, and positioned at the precise address. The procedure of capture, transfer and release of the cell was repeated for other cells, resulting in the formation of pattern with cells. No cell was released from the microcavity during the transfer to the desired position even after the attractive force of p-DEP was switched off. However the use of the microelectrode without the microcavity led to the release of cells trapped at the electrode surface even though cells were directed to the electrode by the attractive force of p-DEP. Therefore, the presence of the microcavity is advantageous to transfer the trapped cells to the desired positions.

Pulsed electrical discharge in conductive solution

Electrical discharge in a conductive solution of isopropyl alcohol in tap water (330 S cm−1) has been studied experimentally applying high voltage millisecond pulses (rise time ∼0.4 , amplitude up to 15 kV, positive polarity) to a pin anode electrode. Dynamic current–voltage characteristics synchronized with high-speed images of the discharge were studied. The discharge was found to develop from high electric field region in the anode vicinity where initial conductive current with density ∼100 A cm−2 results in fast heating and massive nucleation of vapor bubbles. Discharges in nucleated bubbles then produce a highly conductive plasma region and facilitate overheating instability development with subsequent formation of a thermally ionized plasma channel. The measured plasma channel propagation speed was 3–15 m s−1. A proposed thermal model of plasma channel development explains the low observed plasma channel propagation speed.

The structural, optical, ferroelectric properties of (1-x)BiFeO3-xCaTiO3 thin films by a sol–gel method

(1-x)BiFeO3-xCaTiO3 ((1-x)BFO-xCTO, x = 0, 0.05, 0.10, 0.15, 0.20) thin films were successfully grown on Pt(111)/Ti/SiO2/Si(100) substrates using a sol–gel spin coating method. The structure stabilities of BFO thin films were improved by introducing CTO due to the increase of their tolerance factor. The X-ray diffraction patterns indicated that all the samples had a single perovskite structure. The merging phenomenon of (110) and (104) diffraction peaks demonstrated a distortion of the lattice structure in BFO thin films by introducing CTO. The atomic force microscope showed all the samples had dense, crack-free and uniform morphology. The leakage current density decreased with the increasing of CTO contents. At the applied electric field of 300 kV/cm, the leakage current density of the 0.85BFO-0.15CTO was 1.42 × 10−8 A/cm2, which is about 4 orders of magnitude lower than that of the pure BFO thin film (5.78 × 10−4 A/cm2). The leakage conduction mechanism showed Ohmic conduction for all thin films in the low electric field region. In the high electric field region, the leakage mechanisms were dominated by the space-charge-limited current behavior for 0.80BFO-0.20CTO and the Fowler-Norheim tunneling for (1-x)BFO-xCTO (x = 0.10, 0.15) thin films. The remnant polarization (2P r ) and spontaneous polarization (P s ) of (1-x)BFO-xCTO (x = 0.10, 0.15, 0.20) were obviously improved. The 0.85BFO-0.15CTO thin film showed the best ferroelectricity with large remnant polarization of 39.88 μC/cm2 while the remnant polarization of the pure BFO was 3.74 μC/cm2 at the electric field of 300 kV/cm. The absorption edges of (1-x)BFO-xCTO thin films are blue-shift with the increasing of x value. The structural, optical properties and ferroelectricity of BFO thin films were improved by introducing CTO.